Geometrical Effect of a Closed Divertor

We proposed the measure of the degree of divertor closure, δ /λ, where δ the distance from the separatrix to the baffle plate and λ is a scale length of the particle flux. footnote S. Sengoku et al., Bull. Amer. Phys. Soc., 42, 1962 (1997) For a quantitative comparison of the results obtained with various divertors, this measure is better to put together with each data set because even if the data obtained with the same machine or the same divertor configuration, the degree of closure can be varied according to the various plasma configurations, and the data set could vary with this. In the JFT-2M tokamak, the degree of closure has been modified step by step, i.e. δ/λ>>1 (open divertor) arrow δ /λ=1.3 (closed divertor: CD1) arrow δ/λ=0.8 (closed divertor: CD2). In the extremely closed case, CD2, a complete decoupling of divertor and midplane pressures has been realized. This is compared with other configurations.